Field of the Invention
One disclosed aspect of the embodiments relates to a detection apparatus and a detection method for detecting alignment marks formed on an object and a lithography apparatus.
Description of the Related Art
In recent years, high accuracy and high functionality of semiconductor exposure apparatuses have been developed as miniaturization and high integration of semiconductor circuit patterns of integrated circuits (ICs) and large-scale integrations (LSIs) are advanced. In particular, accuracy of alignment of an original, such as a mask or a reticle, and a substrate, such as a semiconductor wafer or a glass plate, is important since the accuracy affects performance of apparatuses. Therefore, a technique of aligning a pattern formed on an original and a shot region set on a substrate with each other in nanometer order has been demanded. Accordingly, a position of the original is required to be exactly obtained.
Alignment of an original relative to an original holding unit (a reticle stage) which holds the original is referred to as “reticle alignment”. In general, the alignment of the original relative to the reticle stage is performed by detecting a reticle mark formed on the original and a reference mark formed on the reticle stage by a scope (a microscope).
Images of the reticle mark and the reference mark are captured by an image pickup element (such as a two-dimensional CCD sensor). The reticle mark and the reference mark enable measurement of positions thereof relative to each other in an alignment direction (a measurement direction). The images of the reticle mark and the reference mark captured by the image pickup element are normally two-dimensional images. Accumulation is performed on each of the two-dimensional images of the reticle mark and the reference mark in a direction orthogonal to the measurement direction (a non-measurement direction) so that a one-dimensional image signal (image data) is generated. As described above, to detect a mark, a method using one-dimensional image data obtained by performing accumulation on a two-dimensional image in the non-measurement direction may be employed (refer to Japanese Patent Laid-Open No. 2004-111861).
However, in a case where dust (foreign particles) adheres on the reticle mark or the reference mark or in a case where a defective portion is included in the reticle mark or the reference mark, when accumulation is performed on each of the two-dimensional images of the marks in the non-measurement direction, a one-dimensional image signal obtained by the accumulation is changed (distorted) due to a factor not associated with the marks. Therefore, accuracy of detection of the marks may be degraded, which affects accuracy of the alignment.